Tubing such as used in heat exchangers often becomes blocked with material such as residue from water.
High pressure water is frequently used to clean the small diameter tubes found in such processing equipment as condensers and heat exchangers which tend to foul and clog with use. The high pressure water is directed against the tube walls with specially designed nozzles attached to the end of long hollow rods called lances. These lances are traversed through the fouled tubes either manually or with automatic devices. Conventional equipment is designed to use the cleaning fluid pressure as the hydraulic force to advance and retract the lance. But because the nozzle supply and the hydraulic supply are not separate systems, the nozzle can not build to high pressures unless the lance movement is mechanically stopped by the presence of a blockage in the tube. Therefore, this system works well to unclog tubes but can not adequately finish cleaning the tubes because of the lack of pressure. The present invention provides a lance which can be traversed while maintaining a high pressure water supply.
The current invention is a modification of the invention described by U.S. Pat. No. 4,225,362. The apparatus described therein consists of a long pipe or casing through which the nozzle, tube, and piston assembly reciprocate. Water is forced into the casing at the front end and applies pressure to the rear of the piston by flowing past the piston's outer diameter. This high pressure water also flows through the hollow piston and into the lance tubing and out the nozzle. As the piston moves forward it creates a vacuum in its wake that must be filled by the water supply and therefore causes a reduction in pressure at the nozzle. This reduced pressure causes a decreased flow through the nozzle and reduced cleaning. When the lance is mechanically stopped by a clog in the tube, the system pressure builds to a maximum.
U.S. Pat. No. 3,791,583 discloses apparatus in which a spray cleaning head is mounted on a reciprocating cleaning fluid supply tube extending from the open end of a hydraulic cylinder An annular piston on the tube, the tube itself, and the cylinder define an expansible chamber within the cylinder. A pump supplies cleaning fluid to the closed end of the hydraulic cylinder, whereby the cleaning fluid exerts pressure on the annular piston, and means are provided for supplying fluid to and draining fluid from the expansible chamber. The pressure exerted by the cleaning fluid on the annular piston moves the supply tube and the cleaning head from a retracted to an extended position when fluid is drained from the expansible chamber, and the supply tube and cleaning head are moved back to the retracted position when fluid is supplied to the expansible chamber.
In the '583 patent, the cleaning fluid is also the fluid which provides pressure for reciprocating the lance. In the present invention, the cleaning fluid pressure is independent of the fluid which provides reciprocating movement of the lance, thereby maintaining the desired fluid pressure to the nozzle through the complete cycle of reciprocation.